| Nowadays, most of the main river systems of China are slightly-polluted, while some city reaches are polluted heavy. The ‘Action of water pollution prevention and control plan’ requires that by 2020, in the seven main watersheds, more than 70% of the rivers’ water quality should be fine(reached or better than the class III) and in prefecture level and above cities’ built-up areas the proportion of malodorous black rivers should be less than 10%. To achieve this goal, it is necessary to control pollutant emission. In addition, the ecological restoration of polluted rivers is indispensable.The study area is the urban part of the Yitong River(the second order tributary of the Songhua River) which is polluted heavy and located in the Changchun City. This study was funded by the project of ‘River ecological restoration technology and demonstration engineering of Yitong River’, which is a sub-project of ‘Chinese National special funds for science and technology for the control and remediation of water pollution’. The concepts of this ecological restoration are ‘close to nature, multi-function, high-efficiency, sustainable’. The stage goal is to ‘increase vitality, improve capacity, reduce pollution, reduce risk’, namely ‘enhance system vitality, improve self-purification ability, reduce pollution load, and reduce the risk of disaster’. Based on the theory of ecology and engineering, this study employed integrated bio-ecological restoration technologies. By doing the engineering design, construction and effects monitoring it constructed the initial engineering technology system of ecological restoration of water pollution and this system can be adapted to the northern climate conditions. Finally, it evaluated the implementation of this restoration project.The research of water ecological restoration in the study area includes three parts:(1) Compound ecological restoration technology of the rural reach. It aims at controlling the agricultural non-point source pollution and soil erosion in the rural area located in the upstream of the urban area;(2) Cascade biological treatment technology. It manages to control the point source pollution of communities which grow fast;(3) Riparian bio-ecological engineering control technology of landscape water. It is designed to treat the slow flow, poor self-purification ability, serious pollution and poor attraction of the urban reach. These three parts constitute the ecological restoration project of water pollution in the urban reach of Yitong River. This research can provide important theoretical basis and technical supports for the ecological restoration of small and medium-sized rivers in the north. The concrete contents and main results are as followings:(1)The ecological restoration project(2009-2011)of non-point source pollution and soil erosion control in the rural reach, implemented in the upstream of urban reach, includes three parts: vegetation buffer strips, multifunction ecological fish pond and river micro-terraforming. The area of the riparian vegetation buffer zone system is 2.30 hm2. Its main function is to filter and intercept the no-point source pollutants from both sides of the farmland, and maintain the stability of the banks and prevent soil erosion. The size of Multifunctional ecological fish pond system is about 1.2 hm2. It takes ‘biological control’ as the working principle and this system is mainly used to coordinate the contradiction between resource utilization, protection and economic development. The area of river micro-terraforming system is 0.7 hm2. It adjusts the beach in the channel and the main function is to purify the upstream, to provide a variety of habitats for fish and other aquatic organisms. By monitoring and evaluating the entrance and exit of the research area before and after the project implementation, it shows that the ecological restoration project can significantly improve the removal rate of BOD5, COD and NH3-N in the river water body. The rate increased from-14.29%、1.81% and-0.5%(2009,before the implementation), respectively, to 66.29%、10.81% and 7.25%(2011, after the implementation). The number of plankton species which can represent clean species increased from 1 to 8. Compared with the implementation of the project, the structure of riparian vegetation community was more intact after two years. The vegetation belt width and the number of species have increased. The average width of herbaceous plants has increased by 36.33 m and its species number has increased ranging from 1 to 6. The width and species number of the shrub belt has increased by 9.12 m and 4 respectively. The average width of arbor belt has increased by 36.33 m, with the increasing species number ranging from 1 to 2. Instead of increasing, the river pollution load has reduced by building the multi-functional ecological fish pond. The removal rate of BOD5 I this fish pond was 9.36%, the COD was cut about 43%, and the DO in the pond was maintained at 8mg/l(with necessary measures for artificial aeration). At the same time, the economic income of operators increased from the original 40000 yuan to about 180000 yuan and the landscape of the fish pond has improved. The results of the implementation show that: This ecological engineering technology system can significantly reduce the surface source pollution of the river, improve the water quality of the urban reach, increase the biological diversity and improve economic benefits of the city. It is an effective technical means to restore the ecological system integrity in the rural areas of northern China and realize the sustainable development of social economy.(2) To prevent and control of the living communities’ point source in the urban area, the ‘4 steps’ ecological management technology was developed. It can reduce the river pollution effectively and is very effective for the heavy pollution and the short process of communities’ sewage tributary. This project was completed in 2011 and covers an area of about 1.2 hm2 which includes four parts: the precipitation interception(24 m2), constructed wetland(1000 m2), the biological filler section(11233 m2) and the plant repair section(30 m2) and the average daily sewage quantity is 360-650 m3(the average is 465 m3). The removal rates of BOD5, TP, TN, COD and NH3-N were 23.77%, 19.17%, 30.18%, 26.38%, 30.96%, respectively. The pollutant removal rates of different parts of this project are different. The constructed wetland has high removal rates of TP(34.71%) and BOD5(35.06%). The removal rates of NH3-N and TN from the biological filling stage were relatively high, which were 45.87% and 37.81% respectively. While the COD removal rate of vegetation was relatively high, the removal rate of COD was 44.32%, and DO increased by 53.86%. Economic benefit analysis shows that the investment of this project is lower than that of the same scale waste water treatment plant at the same time.(3)The riparian auxiliary purification system which is 4.3 hm2 was constructed to improve the problems of the slow flow, poor self-purification ability, riparian hardening and poor attraction in the urban reach. The purification system was built on the original pool of the river bank to purify the river water quality by applying the integrated technology of micro topographic transformation, porous basalt matrix bedding, plant grille with the eco-island construction, ecological water drop, riparian reconstruction, bioremediation and near-natural streams reconstruction. The average daily water treatment is about 9000 m3, which accounts for 3% of the average daily flow of the river and for 20% of the dry season. The removal rates of TP, NH3-N, SS, TN and BOD5 in water were more than 20%. In addition, by focusing on the characteristics of the urban river, landscape diversity and attraction this system is welcomed by citizens.(4) Aiming at the surface source pollution of the upper urban river, this study has constructed a coupling technical system for protecting water environment quality. This system includes riparian vegetation belt system which can intercept the agricultural non-point source pollution, multifunctional fish pond system which can improve aquaculture water pollution and micro terrain adjustment system that can reduce the upper reaches of the water pollution. In the view of the community point source pollution, the technology system of ecological management, including precipitation, wetland, bioremediation technology, was constructed. According to the main river landscape water pollution, the Shore auxiliary purification system which includes sedimentation, filtration, bioremediation, hard straight repair revetment and streams reengineering technology was constructed. The application and implementation of these technologies form the technical system of ecological restoration of the water pollution in the rivers of northern cities. The amount of COD, ammonia nitrogen and total nitrogen in the river was cut down, and the reduction was 330.88×10-3 t/d、17.49×10-3 t/d、30.54×10-3 t/d respectively. It plays a positive role for the increase of self-purification capacity and the restoration of the integrity of the river system. But, in the future, some technologies still need to be improved when they are applied in the process of ecological restoration of river water body, according the characteristics of the river itself, such as the scale of the project, operation maintenance and post management. |
PDF Full Text Request